Spatial synergy of surface •OH and bulk SO4•− in peroxymonosulfate activation over trace Co-hydroxyapatite for efficient water decontamination

Advanced oxidation processes based on peroxymonosulfate (PMS) activation show promising application prospects in the field of water treatment, yet the efficient utilization of reactive oxygen species (ROS) in different spatial regions (bulk solution and catalyst surface) remains challenging. In this work, a catalyst consisting of trace cobalt ion-complexed hydroxyapatite (Co-HAP) was prepared, which exhibits excellent spatial synergistic oxidation effects. Bulk SO 4 •− and in-situ generated surface •OH ensure the efficient removal of levofloxacin (LEV) (74.5% within 20 min). Quenching experiments reveal the surface-mediated ROS evolution pathway, where bulk SO 4 •− reacts with the abundant lattice hydroxyl groups (-OH) on the HAP surface to in-situ generate surface-bound hydroxyl radicals (•OH surf ). Bulk SO 4 •− originates from the activation of PMS by Co ions. Electrochemical characterization and charge density difference simulation confirm that PMS receives electrons from the catalyst, thus inducing the breakage of O-O bonds to generate SO 4 •− . Therefore, bulk SO 4 •− is responsible for attacking dissolved pollutants, while LEV adsorbed on the catalyst surface is "precisely targeted" by surface-confined •OH. This "two-pronged" synergistic strategy significantly reduces mass transfer resistance and achieves efficient utilization of ROS, thereby the degradation rate ( k obs value) of LEV by Co-HAP is 4.6 times that by Co ions alone. Moreover, the Co-HAP system exhibits excellent stability and promising anti-interference ability. This study provides new insights into the positive role of carrier surface functional groups in regulating ROS distribution and evolution in heterogeneous catalysis.